"Ninety-five percent of all victims are rescued by other victims," said earthquake scientist Lucy Jones, who is coordinating the U.S. Geological Survey's Multi-Hazards Demonstration Project. As part of the ShakeOut, about 300 scientists, engineers and economists recently mapped out a disaster scenario in which a magnitude 7.8 earthquake, originating near the Salton Sea, would strike Southern California, with shocks north and west along the San Andreas fault -- and leave Los Angeles without water, power or navigable freeways.

Such an earthquake, they estimate, might cause about 1,800 deaths, 50,000 injuries and $200 billion in damage.

After today's "Duck, Cover and Hold On" drill, nearly 4,000 people from 100 local, state and federal agencies, including the military, in 12 counties in Southern and Central California will rehearse their emergency responses under a statewide program called the Golden Guardian. Gov. Arnold Schwarzenegger launched Golden Guardian in 2004 to improve preparedness for disasters such as terrorist attacks and large toxic spills.

The Golden Guardian exercises will cost about $5 million, to be paid by federal grants, said Jay Alan, spokesman with the governor's Office of Homeland Security. But if practicing helps save lives, it's well worth it, he said.

Across Southern California, numerous emergency facilities will brush up on their disaster response skills.

Organizers will set up a triage center on a football field across the street from Providence Holy Cross Medical Center in Mission Hills -- staffed by doctors, nurses, police, firefighters and volunteers acting as patients. Nearly 300 students from adjacent Bishop Alemany High School will take part, arriving to be treated for a range of potential earthquake injuries such as fractured legs and severed arteries.

At Caltech in Pasadena, two urban search and rescue teams will have to crawl through a maze of cardboard boxes to simulate the experience of extracting survivors in an earthquake. Students will portray victims and emergency crews will treat them for exposure to lab chemicals and spinal injuries.

At Nestle USA's headquarters in Glendale, all 1,600 employees and contractors will participate in the 10 a.m. drill. In addition, a group made up of four employees from each floor of the 21-story building will follow evacuation routes to nearby Incarnation Parish School, where they will rehearse distributing food, water and radio equipment kept at the school in case of disaster.

Around Southern California, cities and government agencies will test their emergency protocols and communication systems.

Experts began gathering Wednesday at the International Earthquake Conference in downtown Los Angeles.

Also downtown, a rally at LA Live on Friday will feature workshops on emergency preparedness.

On Saturday, people can experience the feel of an earthquake in a simulator and stock up on emergency supplies at a fair on the campus of Los Angeles International Charter High School.